The present invention relates to acaricidal compositions, and to methods of use of the compositions to control acarid pests.
Ectoparasites of the genus Acarina, for example ticks, affect cattle, sheep, domestic pets, plants and humans. Many are parasitic, harming the host organisms by appropriating nutrients and metabolites for their own use. In addition, many acarids are vectors for the transmission of diseases, such as tick paralysis and tick toxicosis, sweating sickness, babesiosis (Texas Fever), anaplasmosis, theileriosis and heart water. Such diseases can cause death, morbidity, damaged hides, loss in growth rate, reduction in milk production, and reduction in quality of meat. Thus, acarids can pose a large economic problem in the raising of livestock.
Some acarids, for example cattle ticks, are capable of surviving on grasses in the fields for long periods of time, in the absence of their host animals. The ticks are negatively geotropic, and climb up the grasses. When the host animals are present, the ticks are transferred to them by contact with the grasses. To eliminate ticks from infested pasture land, fields may be burned, crops cultivated, or the fields may be kept free of animals for a number of years. Alternatively, the fields can be treated with chemicals which either kill the ticks or immobilize them. Yet another method is to topically apply chemicals which kill the ticks to the host animals themselves.
Various chemicals have been developed for use against ticks. However, these chemicals lose their efficacy after a period of widespread use due to the spread of resistance among the tick population. For example, arsenic was used to control tick populations from the early 1900's, but prior to World War II the Boophilus spp. ticks developed resistance to arsenic. Later, the organochlorines, DDT, BHC and toxaphene were used to control the arsenic-resistant tick populations. Resistance and unacceptable accumulation of toxic organochlorine residues in meat led to their replacement with organophosphorous and carbamate compounds. These chemicals were then supplanted by formamidines. Because of the seemingly limitless ability of populations to acquire resistance and the dependence of the cattle industry on tick control agents (acaricides) there is a continuing need for new compounds to replace those in the arsenal which are no longer effective.